The development of homogeneous olefin polymerization catalysts has been greatly advanced by the development of reactive cationic transition metal complexes of the type Cp.sub.2 MR.sup.+ X.sup.- (Cp being a cyclopentadienyl-type ligand; M being a Group IVB metal such as titanium, zirconium, or hafnium; R being alkyl, aryl or halide; and X being a weakly coordinating anion). Previously, weakly coordinating anions such as B(C.sub.6 H.sub.3 (3,5CF.sub.3).sub.2).sub.4, B(C.sub.6 F.sub.5).sub.4, RB(C.sub.6 F.sub.5).sub.3, B(C.sub.6 F.sub.4 (4,Si(CH.sub.3).sub.3)).sub.4, and B(C.sub.6 F.sub.4 (4,Si(t-butyl).sub.3)).sub.4. Other such anions are described by Marks et al. in U.S. Pat. No. 5,502,017. Such anions are classified as low interacting anions due to their large size, their ability to spread negative charge over their surfaces and their inert chemical properties. These properties generally decrease the electrostatic attractions between the Cp.sub.2 MR.sup.+ fragment and the anion thus allowing substrates such as olefins to compete favorably for a binding site on the Cp.sub.2 MR.sup.+ fragment. Once such a substrate binds, it reacts with the alkyl group bound to the metal yielding a new longer alkyl chain.
Despite the success of polymerization catalysts of the type Cp.sub.2 MR.sup.+ X.sup.-, further developments including improvements of the weakly coordinating anion have been continually sought. Larger anions are one desired development. Additionally, preparation of the anion should not be a complex multiple step process.
Ludovici et al. describe the synthesis of various pentafluorophenyl gallium derivatives in Journal of Organometallic Chemistry, vol. 441, pp. 363-371 (1992). While preparation of a tetrakis(pentafluorophenyl) gallate species is described, namely tetrabutylammonium tetrakis(pentafluorophenyl) gallate, there is no suggestion of using gallate species in catalysis and the exemplified species would not be suitable in the preparation of trityl catalysts.
It is an object of the present invention to provide a non-boron based salt suitable for preparation of catalysts including a non-boron salt based on gallium, e.g., a trityl based catalyst.
It is a further object of the invention to provide a one step process for preparation of the gallium based salts.
A still further object of the present invention is to provide bridged anionic species including at least two metal atoms such as gallium.
Yet another object of the present invention is to provide organoalumoxane-free ionic polymerization catalyst compositions.